Dufaycolor used a screen with a regular grid of red, blue and green filters permanently fixed to the reverse side of a cellulose acetate film base. The screen was rotated to reduce moiré effects. It was a modified version of dioptichrome, a process for glass plates invented by Louis Dufay in 1907. Dufaycolor was first introduced in 1932 for 16 mm motion picture film, then in 1935 for still photography. Since the screen was part of the film, exposed film was developed using a reversal process. (A negative-positive process was eventually introduced for use in commercial motion pictures, for which reversal processing was not ideal). For still photography Dufaycolor film was often placed between glass plates, as in this example (Pénichon 2013). Dufaycolor was discontinued in 1958.